Tilt tray sorters are employed where it is necessary to sort a stream of incoming parcels to a number of different destinations. Individual tilt tray carriages are linked together into a looped train which is supported on a closed loop track. Discharge stations are located adjacent inclined chutes around the track. Each discharge station corresponds to a particular destination or sorting category of the conveyed parcel. Each carriage receives a parcel at a load station. As parcels are loaded on a particular carriage, a digital controller is supplied with data to indicate the destination chute at which the parcels are to be unloaded. As the train advances around the track, air operated tippers engage the tiltable tray of a carriage when it reaches its programmed destination. The tilted tray discharges the carriage contents onto the inclined chute and then returns to an upright position. The discharged parcels may then proceed to additional processing steps, while the empty carriage returns to the load station to receive a new parcel.
The earliest tilt tray sorters used mechanical chain drives. Such drives offered the benefits of secure physical connection between the drive and the carriage, and represent a very old and well-understood technology. Mechanical chain drive type tilt tray sorters have been used at a number of locations for decades. For example, the United States Postal Service (USPS) has over 20 bulk mail centers, each with a number of tilt tray sorter installations.
Advancements in conveyor technology have made the LIM drive particularly suited for use in tilt tray sorters. In a linear induction motor drive, the train of carriages is still supported on a looped track, but the carriages do not make physical contact with the drive. Instead, the drive motors are fixed, and act on ferromagnetic carrier plates connected to each carriage. The drive motors are positioned at intervals around the track and accelerate the carriages as they pass over. The LIM drives offers the advantages of reduced noise levels, increased reliability as failure of any individual LIM drive motor will not cause the train to halt, and improved system life. A LIM drive motor is extremely reliable, as it contains no moving parts. Although new tilt tray sorter installations can be designed as LIM drive systems, there remain the many current mechanical drive technology installations which represent a significant investment not only in tracks and supports, but in tilt tray carriages. The USPS alone, for example, has tens of thousands of tilt tray carriages, representing an investment of many millions of dollars.
What is needed is a mechanism which permits the rapid and cost-effective conversion of mechanical drive tilt tray sorters to LIM drive sorters.